MongoDB on EC2 Best Practices` To ensure robustness, a 3-node replica set is recommended for MongoDB users on EBS, with nodes distributed across two regions to minimize data loss in case of regional outages. During steady state, one node takes over as primary if the other fails, and a secondary region's node can take over if the primary fails, ensuring data availability. If the entire east coast region is lost, data is still available on the west coast node with a lower priority, allowing for easy migration to that region if needed.